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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces SH/T 1489-1998 Petroleum p-xylene - Determination of purity and hydrocarbon impurities - Gas chromatographic method.
The following main changes have been made with respect to SH/T 1489-1998:
——The calibration area normalization method and related contents are added (see 3.2 and 7.3);
——The scope of this standard is modified (see Clause 1; Clause 1 of Edition 1998);
——The type and specification of capillary chromatographic column are modified and the packed column in the original standard is deleted (see Table 1 in 5.2; Table 1 in 5.1 of Edition 1998);
——Typical chromatographic operating conditions are modified (see Table 1 in 5.2; Table 1 in 5.1 of Edition 1998);
——Specifications of microinjector and volumetric flask are modified (see 5.3~5.5; 5.3~5.5 of Edition 1998);
——Sampling provisions are modified (see Clause 6; Clause 6 of Edition 1998);
——The preparation of calibration solution by internal standard method is modified (see 7.2.1; 7.2.1~7.2.3 of Edition 1998);
——The repeatability limit is modified and reproducibility limit is added (see Clause 9; Clause 9 of Edition 1998);
——Names of some clauses are modified (see Clauses 3, 6, 8 and 11; Clauses 3, 6, 8 and 11 of Edition 1998);
——The quality assurance and control are added (see Clause 10).
This standard was proposed by China Petrochemical Corporation.
This standard is under the jurisdiction of Subcommittee on Petrochemistry of National Technical Committee on Chemical of Standardization Administration of China (SAC/TC63/SC4).
The previous editions of this standard are:
SH/T 1489-1989; SH/T 1489-1998.
Petroleum p-xylene - Determination of purity and hydrocarbon impurities - Gas chromatography
Warning: This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory provisions.
1 Scope
This standard specifies the determination of purity and hydrocarbon impurities of petroleum p-xylene by gas chromatography.
It is applicable to p-xylene with determination purity not less than 99% (mass fraction) and the detection limit of this standard to hydrocarbon impurities such as non-aromatic hydrocarbon, benzene, toluene, ethylbenzene, m-xylene, o-xylene, cumene and p-diethylbenzene is 0.001% (mass fraction).
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 3723 Sampling of chemical products for industrial use - Safety in sampling
GB/T 6678 General principles for sampling chemical products
GB/T 6680 General rules for sampling liquid chemical products
GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values
3 Principle
3.1 Internal standard method
Add a certain amount of internal standard to the specimen and mix well. Under the conditions specified in this standard, inject a proper amount of specimen containing internal standard into a chromatograph equipped with a flame ionization detector (FID). Separate p-xylene from each impurity component effectively on the chromatographic column, measure the peak area of each impurity and internal standard, and calculate the content of each impurity by the internal standard method, then subtract the obtained total amount of impurities from100% to obtain the purity of p-xylene.
3.2 Calibration area normalization method
Under the conditions specified in this standard, inject a proper amount of specimen into a chromatograph equipped with a flame ionization detector (FID). Separate p-xylene from each impurity component effectively on the chromatographic column and measure the peak areas of all components. Calculate the purity of p-xylene and contents of various impurities according to the effective carbon number by calibration area normalization method.
4 Reagents and materials
4.1 Carrier gas: nitrogen, with purity not less than 99.99% (volume fraction), dried and purified by silica gel and 5A molecular sieve.
4.2 Auxiliary gas: nitrogen, with purity not less than 99.99% (volume fraction), dried and purified by silica gel and 5A molecular sieve.
4.3 Burning gas: hydrogen, with purity not less than 99.99% (volume fraction), dried and purified by silica gel and 5A molecular sieve.
4.4 Oxidant gas: air, dried and purified by silica gel and 5A molecular sieve.
Caution: All the above gases are high-pressure compressed gases or extremely flammable gases, so take safety precautions when using them.
4.5 High purity p-xylene: with purity not less than 99.999% (mass fraction).
Generally, the purity of p-xylene obtained is less than 99.9% (mass fraction), and it can be purified by recrystallization. Put a certain amount of p-xylene in an explosion-proof freezer at (-10±5)℃ until approximately 1/2 to 3/4 of the p-xylene is crystallized. Remove the specimen and decant the liquid portion, the remaining crystal portion is purified p-xylene. Allow the p-xylene crystal to thaw and repeat the crystallization step until no impurity peak occurs as indicated by gas chromatography.
4.6 Standard reagents: used for preparation of calibration solution or quality control sample, including n-nonane, benzene, toluene, ethylbenzene, o-xylene, m-xylene, cumene and p-diethylbenzene, with purity not less than 99% (mass fraction).
4.7 Internal standard: n-undecane, with purity not less than 99% (mass fraction). Other compounds meeting the analysis requirements may also be used as internal standards.
Caution: All above substances are flammable or toxic liquids, so take safety precautions when using them.
5 Apparatus
5.1 Gas chromatograph
Any chromatograph having a flame ionization detector; it shall generate a peak height for the hydrocarbon at the minimum determination concentration of at least twice the height of noise and its dynamic linear range meets the quantitative requirements.
5.2 Chromatographic column
See Table 1 for the recommended chromatographic columns and typical operating conditions. Other chromatographic columns and chromatographic conditions that are capable of realizing separation requirements may also be used.
Table 1 Recommended chromatographic columns and typical operating conditions
Chromatographic column Bonded (crosslinked) polyethylene glycol column
Material of column tubing Fused silica
Column length/m 60
Internal diameter of column/mm 0.32
Liquid film thickness/μm 0.50
Carrier gas N2
Carrier gas flow/(mL/min) 1.0
Column temperature Initial temperature/℃
Retention time/min
Temperature rise rate/(℃/min)
Final temperature/℃
Retention time/min 60
10
5
150
10
Temperature of vaporizing chamber/℃ 270
Temperature of detector/℃ 300
Injection volume/μL 0.4
Split ratio 100:1
Note: If the sample contains heavy components of more than ten carbon atoms, the "final temperature" can be appropriately increased to separate the heavy components.
5.3 Recorder
Chromatographic working station or integrator.
5.4 Injector
10μL microinjector or automatic liquid sample injector.
5.5 Volumetric flask
50mL.
5.6 Analytical balance
With sensitivity of 0.1mg.
6 Sample
Take samples in accordance with the safety and technical requirements specified in GB/T 3723, GB/T 6678 and GB/T 6680.
7 Procedure
7.1 Preparation of apparatus
Follow the instructions for mounting and conditioning the chromatographic column into the chromatograph and adjusting the apparatus to the recommended conditions described in Table 1, allowing sufficient time for the apparatus to reach equilibrium before testing.
7.2 Internal standard method
7.2.1 Preparation of standard solution
Add a proper amount of high purity p-xylene and various impurity components, as well as the right amount of internal standard into a 50mL clean and dry volumetric flask, shake well, and weigh to 0.0001g. Calculate the content of each impurity and internal standard, to the nearest 0.0001%. The purity and hydrocarbon impurity content of the prepared p-xylene shall be similar to those of the specimen to be tested, and the p-xylene can be diluted step by step if necessary.
Foreword i
1 Scope
2 Normative references
3 Principle
4 Reagents and materials
5 Apparatus
6 Sample
7 Procedure
8 Test data processing
9 Precision
10 Quality assurance and control
11 Test report
